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Virology

Viruses are obligate, submicroscopic, intracellular parasites that depend upon living cells for their reproduction and cannot propagate in the absence of living cells. All known viruses are infective agents, are often host specific, and in some cases have a high specificity for certain tissues. The isolation and identification of viruses is an elaborate process and requires sophisticated equipment. New methods continue to be developed, but there are several standard techniques used for laboratory diagnosis of viral infections. Many methods utilize in vitro cell culture (tissue culture) systems which are susceptible to cytopathological effects (CPE) from the virus. (Nelson,1992)

The prevention and control of fish viral diseases can be serious problems, especially among cultured (hatchery) fish (Post, 1987). As there are no antibiotic or chemotherapeutic compounds currently available which are effective treatments; quarantine, restriction of movement, slaughter, and/or sanitation and disinfection are the only practical methods of control.

One of California-Nevada Fish Health Center’s primary concern’s is Infectious Hematopoietic Necrosis Virus (IHNV). This virus historically exists in the Sacramento River watershed, and effects chinook salmon and rainbow trout (Piper, 1992). IHNV predominately attacks young salmonids, causing symptoms such as darkened pigment, “pop-eye,” and bleeding at the base of the fins, causing significant die offs of young fish. The virus is transmitted directly from fish to fish or on the egg surface from the parent. Disinfection of eggs with iodine eliminates the parent-egg transmission.

Other viruses of concern are Infectious Pancreatic Necrosis Virus and Viral Hemorrhagic Septicemia.

Nelson, Richard C. et al. 1992. Introduction to Fish Health. U.S. Fish & Wildlife Service.

Piper, Robert G., et al. 1992. Fish Hatchery Management. U.S. Fish & Wildlife Service.

Post, George. 1987. Textbook of Fish Health. T.F.H. Publications, Neptune City, NJ.